Helical-chain copper(II) complexes and a cyclic tetranuclear copper(II) complex with single syn-anti carboxylate bridges and ferromagnetic exchange interactions

Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.     

Synthesis,structure, and DNA cleavage activity of new trinuclear Zn(3) and Zn(2)Cu complexes of a chiral macrocycle: structural correlation with the active center of P1 nuclease

New homo trinuclear Zn(II) complexes [Zn(3)L(1)(micro-OAc)](ClO(4))(2).3CHCl(3).H(2)O, 1, and [Zn(3)L(1)(micro-OAc)].ClO(4).PF(6).5CH(3)OH.H(2)O, 2, and hetero trinuclear complex [Zn(2)CuL(1)(micro-OAc)](ClO(4))(2).3CHCl(3).H(2)O,3, of optically active hexaaza triphenolic macrocycle H(3)L(1) were synthesized and crystallographically characterized. The cation [Zn(3)L(1)(micro-OAc)](+) structure of 1 and 2 closely resembles the trinuclear Zn(II) active site of P1 nuclease. The distorted tetrahedral geometry of Zn3 was successfully reproduced at Cu1 in complex 3. The complexes 2 and 3 cleave CT DNA at 37 and 50 degrees C.     

Cd(II), Zn(II), and Pd(II) complexes of an isoindoline pincer ligand: consequences of steric crowding

The sterically crowded isoindoline pincer ligand, 6'-MeLH, prepared by condensation of 4-methyl-2-aminopyridine and phthalonitrile, exhibits very different reaction chemistry with Cd2+, Zn2+, and Pd2+. Three different ligand coordination modes are reported, each dependent upon choice of metal ion. This isoindoline binds to Cd2+ as a charge-neutral, zwitterionic, bidentate ligand using imine and pyridine nitrogen atoms to form the eight-coordinate fluxional complex, Cd(6'-MeLH)2(NO3)2. In the presence of Zn2+, however, loss of a pyridine arm occurs through solvolysis and tetrahedrally coordinated complexes are formed with coordination of pyrrole and pyridine nitrogen atoms. Reaction with Pd2+ produces the highly distorted, square planar complex Pd(6'-MeL)Cl in which a deprotonated isoindoline anion coordinates as a tridentate pyridinium NNC pincer ligand.     

Size discrimination in the coordination chemistry of an isoindoline pincer ligand with CdII and ZnII

The reactions of Cd2+ and Zn2+ with the pyridine-arm isoindoline ligand 4'-MeLH = 1,3-bis[2-(4-methylpyridyl)imino]isoindoline produced the series of octahedrally coordinated complexes M(4'-MeL)2, [M(4'-MeLH)2]2+, and [M(4'-MeL)(4'-MeLH)]+. The complexes M(4'-MeL)2 resulted from reactions of the respective metal perchlorates with deprotonated ligand, whereas the complexes [M(4'-MeLH)2](ClO4)2 resulted from reactions with ligand in the absence of added base. The mixed-ligand complexes [M(4'-MeL)(4'-MeLH)]+ were generated in solution by reactions of equimolar quantities of M(4'-MeL)2 and [M(4'-MeLH)2]2+. Whereas [Cd(4'-MeL)(4'-MeLH)]+ is stable in solution, [Zn(4'-MeL)(4'-MeLH)]+ converts to and establishes equilibrium with the tetrahedrally coordinated, trinuclear complex [Zn3(4'-MeL)4]2+. The complexes Cd(4'-MeL)2 (1), Zn(4'-MeL)2 (2), and [Cd(4'-MeL)(4'-MeLH)]ClO4 (5) were characterized by single-crystal X-ray diffraction, with the latter complex being shown to contain 4'-MeLH coordinated as a protonated iminium zwitterionic ligand. The [M(4'-MeLH)2]2+ and [M(4'-MeL)(4'-MeLH)]+ complexes are tautomeric in solution because of the shuttling of the iminium protons between imine N atoms. The rate of prototropic tautomerism in [Cd(4'-MeLH)2]+ was followed by 1H NMR spectroscopy. Over the temperature range 276-312 K, a linear Eyring plot with the activation parameters DeltaG++ = 16.0 +/- 0.1 kcal/mol, DeltaH++ = 2.9 +/- 0.1 kcal/mol, and DeltaS++ = -44.0 +/- 0.3 cal/mol.K was obtained.     

A mononuclear, mixed (salicylato) (nicotinamide) complex of Zn(II) with penta- and hexa-coordination sites: a novel framework structure

The title compound, diaqua(bissalicylato-??O)(bisnicotinamide-??N)zinc(II)][bis(triaqua (monosalicylato-??O)(mononicotinamide-??N)zinc(II)salicylate, includes three Zn(II) ions, four nicotinamide ligands, six salicylate ligands and eight coordinated aqua ligands in the asymmetric unit in complex structure. The geometry around one of the Zn(II) ions is a slightly distorted octahedron, of which the equatorial plane is formed by two carboxylate oxygens and two aqua oxygens, while the axial positions are occupied by two pyridyl nitrogen atoms. The other Zn(II) ions adopt fivefold coordinations with one carboxylate oxygen atom from salicylate ligand, one N atom from nicotinamide ligand and three oxygen atoms from aqua ligands. In addition, there are two salicylate anions in the unit cell that are not coordinated. They provide charge balance as counter-ions in the complex framework.     

Ferromagnetic coupling in trinuclear, partial cubane Cu(II) complexes with a micro(3)-OH core: magnetostructural correlations

Three new trinuclear copper(II) complexes, [(CuL(1))(3)(micro(3)-OH)][ClO(4)](2).3 H(2)O (1), [(CuL(2))(3)(micro(3)-OH)][ClO(4)](2).H(2)O (2), and [(CuL(3))(3)(micro(3)-OH)][ClO(4)](2).7 H(2)O (3) have been synthesized from the three tridentate Schiff bases HL(1), HL(2), and HL(3) (HL(1)=6- aminomethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one, HL(2)=6-aminoethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one, and HL(3)=6-aminodimethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one). They have been characterized by X-ray crystallography and IR and UV spectroscopy, and their magnetic properties have been investigated. All the compounds contain a partial cubane [Cu(3)O(4)] core consisting of the trinuclear unit [(CuL)(3)(micro(3)-OH)](2+), perchlorate ions, and water molecules. In each of the complexes, the copper atoms are five-coordinate with a distorted square-pyramidal geometry except complex 1, in which one of the Cu(II) of the trinuclear unit is weakly coordinated to one of the perchlorate ions. Magnetic measurements performed in SQUID MPMS-XL7 using polycrystalline samples at an applied field of 2 kOe indicate a global intramolecular ferromagnetic coupling. Magnetostructural correlations have been calculated on the basis of theoretical models without symmetry restriction. Continuous shape measurements are an appropriate tool for establishing the degree of distortion of the Cu(II) from square-planar geometry. Structural, theoretical, and experimental magnetic data indicate that the higher the degree of distortion, the greater the ferromagnetic coupling.     

Sulfur-rich zinc chemistry: new tris(thioimidazolyl)hydroborate ligands and their zinc complex chemistry related to the structure and function of alcohol dehydrogenase

The 1-substituted tris(2-thioimidazolyl)hydroborate ligands Tt(R) were prepared as the potassium salts from KBH(4) and the corresponding 1-R-2-thioimidazole for R = t-Bu and C(6)H(4)-p-CH(CH(3))(2) (Cum). Their reactions with zinc salts yielded the tetrahedral complexes Tt(R)Zn-X with X = F, Cl, ONO(2) and (Tt(t)()(-)(Bu))(2)Zn. With zinc perchlorate the labile perchlorate complexes Tt(R)Zn-OClO(3) were obtained. They served as starting materials for the incorporation of substrates which are relevant for the chemistry of horse liver alcohol dehydrogenase: Ethanol led to [Tt(t)()(-Bu)Zn.EtOH] ClO(4).EtOH, p-nitrophenol (NitOH) yielded Tt(Cum)Zn-ONit. Pyridine-2-carbaldehyde and salicylic aldehyde were incorporated as N(pyridine) and O(phenolate) coligands with possible additional O(aldehyde) coordination. Substituted pyridyl methanols (R-PyCH(2)OH) yielded the trinuclear complexes [(Tt(t)()(-Bu))(2)Zn(3)(R-PyCH(2)O)(2)] (ClO(4))(2) with bridging Tt and pyridylmethoxide ligands. Preliminary experiments on the functional modeling of alcohol dehydrogenase have shown that TtZn complexes promote both the dehydrogenation of 2-propanol and the hydrogenation of pentafluorobenzaldehyde.     

Solid-state and solution-state coordination chemistry of the zinc triad with the mixed N,S donor ligand bis(2-methylpyridyl) sulfide

The binding of group 12 metal ions to bis(2-methylpyridyl) sulfide (1) was investigated by X-ray crystallography and NMR. Seven structures of the chloride and perchlorate salts of Hg(II), Cd(II), and Zn(II) with 1 are reported. Hg(1)(2)(ClO(4))(2), Cd(1)(2)(ClO(4))(2), and Zn(1)(2)(ClO(4))(2).CH(3)CN form mononuclear, six-coordinate species in the solid state with 1 binding in a tridentate coordination mode. Hg(1)(2)(ClO(4))(2) has a distorted trigonal prismatic coordination geometry while Cd(1)(2)(ClO(4))(2) and Zn(1)(2)(ClO(4))(2).CH(3)CN have distorted octahedral geometries. With chloride anions, the 1:1 metal to ligand complexes Hg(1)Cl(2), [Cd(1)Cl(2)](2), and Zn(1)Cl(2) are formed. A bidentate binding mode that lacks thioether coordination is observed for 1 in the four-coordinate, distorted tetrahedral complexes Zn(1)Cl(2) and Hg(1)Cl(2). [Cd(1)Cl(2)](2) is dimeric with a distorted octahedral coordination geometry and a tridentate 1. Hg(1)Cl(2) is comprised of pairs of loosely associated monomers and Zn(1)Cl(2) is monomeric. In addition, Hg(2)(1)Cl(4) is formed with alternating chloride and thioether bridges. The distorted square pyramidal Hg(II) centers result in a supramolecular zigzagging chain in the solid state. The solution (1)H NMR spectra of [Hg(1)(2)](2+) and [Hg(1)(NCCH(3))(x)()](2+) reveal (3)(-)(5)J((199)Hg(1)H) due to slow ligand exchange found in these thioether complexes. Implications for use of Hg(II) as a metallobioprobe are discussed.     

Reactivity of mu-hydroxodizinc(II) centers in enzymatic catalysis through model studies

The stable dinuclear complex [Zn2(BPAM)(mu-OH)(mu-O2PPh2)](ClO4)2, where BPAN = 2,7-bis[2-(2-pyridylethyl)-aminomethyl]-1,8-naphthyridine, was chosen as a model to investigate the reactivity of (mu-hydroxo)dizinc(II) centers in metallohydrolases. Two reactions, the hydrolysis of phosphodiesters and the hydrolysis of beta-lactams, were studied. These two processes are catalyzed in vivo by zinc(II)-containing enzymes: P1 nucleases and beta-lactamases, respectively. The former catalyzes the hydrolysis of single-stranded DNA and RNA. beta-Lactamases, expressed in many types of pathogenic bacteria, are responsible for the hydrolytic degradation of beta-lactam antibiotic drugs. In the first step of phosphodiester hydrolysis promoted by the dinuclear model complex, the substrate replaces the bridging diphenylphosphinate. The bridging hydroxide serves as a general base to deprotonate water, which acts as a nucleophile in the ensuing hydrolysis. The dinuclear model complex is only 1.8 times more reactive in hydrolyzing phosphodiesters than a mononuclear analogue, Zn(bpta)(OTf)2, where bpta = N,N-bis(2-pyridylmethyl)-tert-butylamine. Hydrolysis of nitrocefin, a beta-lactam antibiotic analogue, catalyzed by [Zn2(BPAN)(mu-OH)(mu-O2PPh2)](ClO4)2 involves monodentate coordination of the substrate via its carboxylate group, followed by nucleophilic attack of the zinc(II)-bound terminal hydroxide at the beta-lactam carbonyl carbon atom. Collapse of the tetrahedral intermediate results in product formation. Mononuclear complexes Zn(cyclen)-(NO3)2 and Zn(bpta)(NO3)2, where cyclen = 1,4,7,10-tetraazacyclododecane, are as reactive in the beta-lactam hydrolysis as the dinuclear complex. Kinetic and mechanistic studies of the phosphodiester and beta-lactam hydrolyses indicate that the bridging hydroxide in [Zn2(BPAN)(mu-OH)(mu-O2PPh2)](ClO4)2 is not very reactive, despite its low pKa value. This low reactivity presumably arises from the two factors. First, the briding hydroxide and coordinated substrate in [Zn2(BPAN)(mu-OH)(substrate)]2+ are not aligned properly to favor nucleophilic attack. Second, the nucleophilicity of the bridging hydroxide is diminished because it is simultaneously bound to the two zinc(II) ions.     

Cadmium(II) and mercury(II) complexes of an NO2S2-donor macrocycle and its ditopic xylyl-bridged analogue

The NO2S2-donor macrocycle (L1) was synthesised from the ring closure reaction between Boc-N-protected 2,2'-iminobis(ethanethiol) (3) and 2,2'-(ethylenedioxy)bis(benzyl chloride) (4) followed by deprotection of the Boc-group. alpha,alpha'-Dibromo-p-xylene was employed as a dialkylating agent to bridge two L1 to yield the corresponding N-linked product (L2). The X-ray structure of L2 (as its HBr salt) is described. A range of Cd(II) and Hg(II) complexes of L1 (6-9) and L2 (10-12) were prepared and characterised. Reaction of HgX2 (X = Br or I) with L1 afforded [Hg(L1)Br]2[Hg2Br6].2CH2Cl2 6 and [Hg(L1)I(2)] 7, respectively. For 6, the Hg(II) ion in the complex cation has a distorted tetrahedral coordination environment composed of S2N donor atoms from L1 and a bromo ligand. In 7 the coordination geometry is highly distorted tetrahedral, with the macrocycle coordinating in an exodentate manner via one S and one N atom. The remaining two coordination sites are occupied by iodide ions. [Hg(L1)(ClO4)]ClO4 8 was isolated from the reaction of Hg(ClO4)2 and L1. The X-ray structure reveals that all macrocyclic ring donors bind to the central mercury ion in this case, with the latter exhibiting a highly distorted octahedral coordination geometry. The O2S2-donors from the macrocyclic ring define the equatorial plane while the axial positions are occupied by the ring nitrogen as well as by an oxygen from a monodentate perchlorato ion. Reaction of Cd(NO3)(2).4H2O with L1 afforded [Cd(L1)(NO3)2](.)0.5CH2Cl2 9 in which L1 acts as a tridentate ligand, binding exo-fashion via its S2N donors. The remaining coordination positions are filled by two bidentate nitrate ions such that, overall, the cadmium is seven-coordinate. Reactions of HgX2(X = Br or I) with L2 yielded the isostructural 2 : 1 (metal : ligand) complexes, [Hg2(L2)Br4] 10 and [Hg2(L2)I(4)] 11. Each mercury ion has a distorted tetrahedral environment made up of S and N donors from an exodentate L2 and two coordinated halides. Contrasting with this, the reaction of L2 with Cd(NO3)(2).4H2O yielded a 1-D coordination network, {[Cd2(L2)(NO3)4].2CH2Cl2}n 12 in which each ring of L2 is exo-coordinated via two S atoms and one N atom to a cadmium ion which is also bound to one monodentate and one bidentate nitrate anion. The latter also has one of its oxygen atom attached to a neighboring cadmium via a nitroso (mu2-O) bridge such that the overall coordination geometry about each cadmium is seven-coordinate. The [Cd(L2)0.5(NO3)2] units are linked by an inversion to yield the polymeric arrangement.     

First halogen anion-bridged (MMX)(n)-type one-dimensional coordination polymer built upon d(10)-d(10) dimers

The complex [Ag(2)(PhPPy(2))(2)(NCCH(3))(2)](ClO(4))(2) [PhPPy(2) = bis(2-pyridyl)phenylphosphine] reacts with NH(4)Cl to form an insoluble one-dimensional polymer of the type (MMX)(n), {[Ag(2)(PhPPy(2))(2)Cl](ClO(4))}(n). The binuclear unit, Ag(2)(PhPPy(2))(2)(2+), exhibits two PhPPy(2) tridentate ligands bridging the two Ag atoms in a head-to-tail fashion with C(2h) symmetry, and the Ag···Ag distance [3.0942(11) ?, X-ray] suggests argentophilic interactions. Each Ag center adopts a distorted trigonal-bipyramidal geometry, coordinated by one P atom and two pyridyl arms at the equatorial positions and interacting with one Cl ion and one Ag ion at the axial positions. The short Ag-Cl bond length [2.5791(7) ?] indicates the presence of some covalent character. The solid-state absorption bands spread all the way to 600 nm have been interpreted by means of density functional theory (DFT) and time-dependent DFT (B3LYP), and the lowest-energy excited states are assigned to metal/halide-to-pyridyl charge transfer, consistent with the d(10) electronic configuration of Ag. The calculated oscillator strengths are low because of the poor molecular orbital overlaps in the charge-transfer components. The novel material exhibits a luminescence band centered at about ～520 nm.     

Bis[3,6-bis(6-methyl-2-pyridyl)pyridazine-κ2N2,N3]chlorocopper(II) perchlorate

The title compound, [CuCl(C₁₆H₁₄N₄)₂]ClO₄, consists of a mononuclear complex cation and a perchlorate anion. The coordination of the copper(II) ion exhibits a trigonal bipyramidal geometry, where the equatorial plane is composed of the Cl atom and two N atoms of the two pyridazine rings, and the axial positions are occupied by the N atoms of two methyl­pyridine rings.     

Bis-qtpy (qtpy = 2,2':6',2'':6'',2'"-quaterpyridine) metal complexes, [M(qtpy)(2)]2+

Reactions of perchlorates of iron(II), nickel(II), and zinc(II) with 2,2':6',2':6',2'"-quaterpyridine (qtpy) gave the first crystallographically established bis-qtpy metal complexes of formula [M(qtpy)(2)][ClO(4)](2) (M = Fe, Ni, Zn). Coordination of two terdentate quaterpyridines to the same center produces a distorted octahedron of six nitrogen atoms around the metal, leaving two pendant pyridyl groups, one for each quaterpyridine. For the diamagnetic zinc system, an NMR investigation has been carried out in order to establish the conditions to obtain the intermediate mono-qtpy complex, of formula [Zn(qtpy)(H(2)O)(2)][ClO(4)](2), which has also been crystallographically established. The corresponding hexafluorophosphate derivatives [M(qtpy)(2)][PF(6)](2) (M = Ni and Zn) were prepared in DMF at room temperature.     

Synthesis and Crystal Structure of Copper(II) Complex with Mixed Bipyridine and 2-Hydroxy-1-naphthaldehyde Ligands

1 INTRODUCTION Galactose oxidase is a monomeric enzyme that catalyzes the stereospecific oxidation of a broad range of primary alcohol substrates and possesses a unique mononuclear copper site essential for catalyzing a two-electron transfer reaction during the oxidation of primary alcohol to corresponding aldehydes[1]. The catalytic reaction is shown in Eq. 1. RCH2OH + O2 RCHO + H2O2 (1) A recent report on the crystal structure of galactose oxidase reveals a unique mo…     

Structural features of mono- and tri-nuclear Zn(II) complexes with a non-steroidal anti-inflammatory drug as ligand

The interaction of Zn(II) with the non-steroidal anti-inflammatory drug tolfenamic acid leads to the formation of the structurally characterized trinuclear [Zn(3)(tolfenamato)(6)(CH(3)OH)(2)] complex. In the presence of the N,N'-donor heterocyclic ligands 1,10-phenanthroline and 2,2'-bipyridine at a range of ratios, the mononuclear Zn complexes of the general formulae [Zn(tolfenamato)(N,N'-donor)Cl] and [Zn(tolfenamato)(2)(N,N'-donor)] have been isolated and structurally characterized by X-ray crystallography. The deprotonated tolfenamato ligands are coordinated to the Zn(II) ion through carboxylato oxygen atoms. Tolfenamic acid and its complexes exhibit good binding propensity to human or bovine serum albumin protein having relatively high binding constant values.     

Macrocyclic copper(II) and zinc(II) complexes incorporating phosphate esters

Slow evaporation of solutions prepared by adding either Cu(ClO(4))(2).6H(2)O or Zn(ClO(4))(2).6H(2)O to solutions containing appropriate proportions of Me(3)tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) and sodium phenyl phosphate (Na(2)PhOPO(3)) gave dark blue crystals of [Cu(3)(Me(3)tacn)(3)(PhOPO(3))(2)](ClO(4))(2).(1)/(2)H(2)O (1) and colorless crystals of [Zn(2)(Me(3)tacn)(2)(H(2)O)(4)(PhOPO(3))](ClO(4))(2).H(2)O (2), respectively. Blue crystals of [Cu(tacn)(2)](BNPP)(2) (3) formed in an aqueous solution of [Cu(tacn)Cl(2)], bis(p-nitrophenyl phosphate) (BNPP), and HEPES buffer (pH 7.4). Compound 1 crystallizes in the triclinic space group P1 (No. 2) with a = 9.8053(2) A, b = 12.9068(2) A, c = 22.1132(2) A, alpha = 98.636(1) degrees, beta = 99.546(1) degrees, gamma = 101.1733(8) degrees, and Z = 2 and exhibits trinuclear Cu(II) clusters in which square pyramidal metal centers are capped by two phosphate esters located above and below the plane of the metal centers. The trinuclear cluster is asymmetric having Cu...Cu distances of 4.14, 4.55, and 5.04 A. Compound 2 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 13.6248(2) A, b = 11.6002(2) A, c = 25.9681(4) A, beta = 102.0072(9) degrees, and Z = 4 and contains a dinuclear Zn(II) complex formed by linking two units of [Zn(Me(3)tacn)(OH(2))(2)](2+) by a single phosphate ester. Compound 3 crystallizes in the monoclinic space group C2/c (No. 15) with a = 24.7105(5) A, b = 12.8627(3) A, c = 14.0079(3) A, beta = 106.600(1) degrees, and Z = 4 and consists of mononuclear [Cu(tacn)(2)](2+) cations whose charge is balanced by the BNPP(-) anions.     

Coordination induced fluorescence enhancement and construction of a Zn3 constellation through hydrolysis of ligand imine arms

The phenoxido and alkoxido bridged neutral Zn(3) complex [Zn(3)(μ-H(2)bemp)(2)(μ(3)-emp)(2)] (1), with an angular Zn(3)(μ-OPh)(2)(μ-OEt)(2) core and capping nitrogen donors, was synthesized via simultaneous chelation-cum-bridging of the parent and hydrolysed ligands. Zinc(II) coordination triggered the solution phase imine (C=N) bond hydrolysis of H(3)bemp (2,6-bis-[(2-hydroxyethylimino)methyl]-4-methylphenol) and yielded the unexpected angular trinuclear Zn(II) complex 1, having structural similarity with the Zn(3) active site of P1 nuclease. H(3)bemp also displays a zinc(II) selective chelation-enhanced fluorescence response from strong metal ion coordination. Complexation of zinc(II) with H(3)bpmp (2,6-bis-[(3-hydroxypropylimino)methyl]-4-methylphenol), a close analogue of H(3)bemp, instead provides only mononuclear [Zn(H(2)bpmpH(N))(2)](ClO(4))(2)·2H(2)O (2·2H(2)O) (H(N) is the proton attached to an imine nitrogen atom) of two zwitterionic ligands, generated through a kind of coordination driven acid-base reaction, without showing any aggregation reaction. As the sole metal-organic precursor, both the complexes under pyrolytic conditions give ZnO nano structures of two morphologies.     

Synthesis and Crystal Structure of a New One-dimensional Zn(II) Nitronyl Nitroxide Complex Bridged by Pyridine-2,4-dicarboxylate Anion

1 INTRODUCTION The synthesis and study of transition metal com- pounds incorporating organic free radicals directly bound to their coordination sphere are a major re- search aim in the field of molecular magnetism[1]. Exceptional stability, ease of chemical modification and versatility in their coordination properties have made nitroxide free radicals one of the most attrac- tive spin carriers for the design of molecular magne- tic materials[2, 3]. The structures and magnetic prope- rties …     

Zn6[MeN(CH2CO2)(CH2PO3)](6)(Zn)]4- anion: the first example of the oxo-bridged Zn6 octahedron with a centered Zn(II) cation

Hydrothermal reactions of N-(phosphonomethyl)-N-methylglycine, MeN(CH(2)CO(2)H)(CH(2)PO(3)H(2)) (H(3)L), with zinc(II) acetate resulted in the formation of a novel zinc carboxylate-phosphonate, [Zn(6)L(6)(Zn)][Zn(H(2)O)(6)](2) x 22H(2)O (1). The structure of 1 contains a heptanuclear zinc phosphonate cluster anion, [Zn(6)L(6)(Zn)](4-), in which seven zinc(II) cations form an unusual Zn(6)(Zn) centered octahedron with six of its Zn(3) triangle faces each further capped by a phosphonate group. The Zn(II) cations of the Zn(6) octahedron are five-coordinated whereas the centered Zn(II) cation is octahedrally coordinated. Packing of these cluster anions creates micropores occupied by the hydrated zinc(II) cations as well as lattice water molecules. The structural skeleton of 1 is retained after the removal of the lattice water molecules.     

Coordination chemistry of mercury(II) in liquid and aqueous ammonia solution and the crystal structure of tetraamminemercury(II) perchlorate

The ammonia solvated mercury(II) ion has been structurally characterized in solution by means of EXAFS, (199)Hg NMR, and Raman spectroscopy and in solid solvates by combining results from X-ray single crystal and powder diffraction, thermogravimetry, differential scanning calorimetry, EXAFS, and Raman spectroscopy. Crystalline tetraamminemercury(II) perchlorate, [Hg(NH3)4](ClO4)2, precipitates from both liquid ammonia and aqueous ammonia solution, containing tetraamminemercury(II) complexes. The orthorhombic space group ( Pnma) imposes C s symmetry on the tetraamminemercury(II) complexes, which is lost at a phase transition at about 220 K. The Hg-N bond distances are 2.175(14), 2.255(16), and 2 x 2.277(9) A, with a wide N-Hg-N angle between the two shortest Hg-N bonds, 122.1(7) degrees , at ambient temperature. A similar distorted tetrahedral coordination geometry is maintained in liquid ammonia and aqueous ammonia solutions with the mean Hg-N bond distances 2.225(12) and 2.226(6) A, respectively. When heated to 400 K the solid tetraamminemercury(II) perchlorate decomposes to diamminemercury(II) perchlorate, [Hg(NH3)2](ClO4)2, with the mean Hg-N bond distance 2.055(6) A in a linear N-Hg-N unit. The mercury atoms in the latter compound form a tetrahedral network, connected by perchlorate oxygen atoms, with the closest Hg...Hg distance being 3.420(3) A. The preferential solvation and coordination changes of the mercury(II) ion in aqueous ammonia, by varying the total NH 3:Hg(II) mole ratio from 0 to 130, were followed by (199)Hg NMR. Solid [Hg(NH 3)4](ClO4)2 precipitates while [Hg(H2O)6](2+) ions remain in solution at mole ratios below 3-4, while at high mole ratios, [Hg(NH3)4](2+) complexes dominate in solution. The principal bands in the vibrational spectrum of the [Hg(NH3)4](2+) complex have been assigned.